AFAIK this can be achieved using a custom template for /var/qmail/control/smtproutes
I don't know exactly what pelli wants or why.
SME server only supports one outbound authenticated email route, configured via the server-manager. To support more than one authenticated outbound route, you would need more than one instance of the smtp auth proxy, as well as a custom template in smtproutes. This is something I expect pelli doesn't actually need, and may not have the skills to do.